1 . Field of the Invention
The invention relates to an oil pump including a rotor that is driven to be rotated, and an outer peripheral member that has a cylindrical shape and that accommodates the rotor.
2 . Description of the Related Art
For example, a conventional oil pump 101 illustrated in FIG. 8 includes: a rotor 130 that is driven to be rotated by a rotary shaft 150 that rotates about a rotation axis Z150 (the rotary shaft 150 is driven to be rotated clockwise in an example illustrated in FIG. 8); an outer peripheral member 140 that has a generally cylindrical shape and that accommodates the rotor 130; a first plate 110 that covers one of end faces of the outer peripheral member 140 (the first plate 110 is disposed on the opposite side of the outer peripheral member 140 from a person who sees FIG. 8 in a direction perpendicular to the sheet on which FIG. 8 is drawn); and a second plate (not illustrated) that covers the other one of the end faces of the outer peripheral member 140 (the second plate is disposed on the side closer to the person who sees FIG. 8). An outer peripheral portion of the rotor 130 is provided with a plurality of vanes 131 urged radially outward, and ten transfer chambers 130V are defined by an outer peripheral face of the rotor 130, an inner peripheral face of the outer peripheral member 140, the first plate 110, the second plate, and the vanes 131. As illustrated in FIG. 8, when the rotor 130 rotates clockwise, the volume of each transfer chamber 130V that is passing through a suction region 110K (a suction region 111k) including a suction port 110in (a suction port 111in) gradually increases and hydraulic fluid is sucked in through the suction port 110in (the suction port 111in). At the same time, the volume of each transfer chamber 130V that is passing through a discharge region 110T (a discharge region 111T) including a discharge port 110ex (a discharge port 111ex) gradually decreases and the hydraulic fluid is discharged to the discharge port 110ex (the discharge port 111ex). A sealed region 110F (a sealed region 111F) is a region extending from the end point of the suction port 110in (the suction port 111in) to the start point of the discharge port 110ex (the discharge port 111ex). The transfer chamber 130V that has reached the end point of the suction port 110in (the suction port 111in) passes through the sealed region 110F (the sealed region 111F) before reaching the start point of the discharge port 110ex (the discharge port 111ex) as the rotor 130 rotates. The volume of each transfer chamber 130V that is passing through the sealed region 110F (the sealed region 111F) is kept nearly unchanged.
When the transfer chamber 130V reaches the discharge region 110T (the discharge region 111T) after passing through the sealed region 110F (the sealed region 111F), the hydraulic fluid at high pressure suddenly flows into the transfer chamber 130V from the discharge port 110ex (the discharge port 111ex), so that the pressure of the hydraulic fluid in the transfer chamber 130V abruptly increases. As a result, cavitation, which is a phenomenon in which air bubbles are generated and disappear, is likely to occur. Occurrence of cavitation should be avoided, because it may be a factor of generation of noise and erosion. Therefore, a pressure gradually-changing groove 110M (a pressure gradually-changing groove 111M) is formed in each of the first plate 110 and the second plate. The hydraulic fluid from the discharge port 110ex (the discharge port 111ex) is gradually supplied into the transfer chamber 130V that is passing through the sealed region 110F (the sealed region 111F) to avoid an abrupt increase in the pressure of the hydraulic fluid in the transfer chamber 130V. The pressure gradually-changing grooves formed in the first plate 110 and the pressure gradually-changing grooves formed in the second plate are opposed to each other.
Japanese Patent Application Publication No. 2009-209817 (JP 2009-209817 A) describes an oil pump in which a shallow bottom portion and a V-shaped valley portion (corresponding to the pressure gradually-changing groove) are formed at a position adjacent to the start point of a discharge port of a pump casing, in the sealed region 110F (the sealed region 111F) illustrated in FIG. 8. In this oil pump, it is possible to more reliably prevent erosion.
JP 2009-209187 A does not clearly describe whether the shallow bottom portion and the V-shaped valley portion are formed on each of both end face sides of an inner rotor and an outer rotor, and thus it may be deemed that they are formed on one of the end face sides. Even if they are formed on each of both end face sides, it may be deemed that the shallow bottom portion and the V-shaped valley portion have the same sizes and shapes. In order to reliably prevent erosion, it is preferable to cause the hydraulic fluid at high pressure to flow from the discharge port into each transfer chamber from both end face sides, instead of causing the hydraulic fluid at high pressure to flow from the discharge port into each transfer chamber from one end face side. However, if the hydraulic fluid at high pressure is simply introduced from the suction port into each transfer chamber from the both end face sides, the pressure difference between the hydraulic fluid introduced from one end face side and the hydraulic fluid introduced from the other end face side becomes large, and such large pressure difference may promote occurrence of cavitation. In a state where dynamic flow of hydraulic fluid is caused in an oil pump rotating at a high speed, even if the pressure gradually-changing grooves (or shallow bottom portions and the V-shaped valley portions) are formed in the same shape and size, a pressure difference may be caused due to various factors.